The present invention relates to vacuum lifting devices in general, and more particularly to a vacuum lifting arrangement for flat workpieces, such as lumber boards, lumber planks and the like.
There are already known various constructions of vacuum lifting arrangements of the above type, among them such which include a vertically and horizontally movable housing which forms a vacuum chamber, and an elastic sealing element arranged on the housing, operative for conformingly contacting the workpiece, and being constituted either by a foamed material mat provided with through suction apertures, or by individual suction cups.
Vacuum lifting arrangements of the above type have been developed in the course of the last 20 or 30 years and they are being further improved. Such lifting arrangements render it possible simultaneously (commonly) to lift a plurality of workpieces which are arranged adjacent to one another, regardless of whether or not free space (air) is present between the workpieces, whether or not the workpieces are cracked or otherwise damaged, whether or not workpieces are missing, and whether or not the workpieces have rough, cracked or soiled surfaces. Arrangements of this type can be used in manually operated installations just as well as in partially or fully motorized or automated applications. These arrangements are primarily being used for handling lumber elements, but they can also be utilized for handling elements of other materials. These arrangements have proven themselves to be particularly well suited for use in sawn lumber processing.
The basic principle of operation of an arrangement of this type involves the known physical phenomena of vacuum technology and of fluid dynamics. The basic construction of the lifting arrangements of this type is such that vacuum generating devices of different constructions can be connected thereto.
Experience with known arrangements of this type has shown, however, that they leave much to be desired in terms of simplicity of construction and also reliability of operation, since in many instances surface discontinuities in the workpieces to be lifted render the entire arrangement ineffective.